A river is a natural flow of running water that follows a well-defined, permanent path, usually within a valley. A stream (also called a brook or a creek) is a natural flow of water that follows a more temporary path that is usually not in a valley. However, the term stream is often used to mean any natural flow of water, including rivers. Although some rivers are larger than some streams, size is not a distinguishing factor.

The origin of a river or stream is called its source. If its source consists of many smaller streams coming from the same region, they are called its headwaters. Its channel is...